Mysql将单条记录中一个字段拆分为单个

/*
 Navicat Premium Data Transfer
 Source Server         : springcloud
 Source Server Type    : MySQL
 Source Server Version : 50736
 Source Host           : localhost:3306
 Source Schema         : atguigudb
 Target Server Type    : MySQL
 Target Server Version : 50736
 File Encoding         : 65001
 Date: 12/08/2022 11:54:38
*/
SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;
-- ----------------------------
-- Table structure for book
-- ----------------------------
DROP TABLE IF EXISTS `book`;
CREATE TABLE `book`  (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(20) CHARACTER SET utf8mb4 COLLATE utf8mb4_bin NULL DEFAULT '',
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = MyISAM AUTO_INCREMENT = 6 CHARACTER SET = utf8mb4 COLLATE = utf8mb4_bin ROW_FORMAT = Dynamic;
-- ----------------------------
-- Records of book
-- ----------------------------
INSERT INTO `book` VALUES (1, 'a,B,C,D');
INSERT INTO `book` VALUES (2, 'a,B,C,D');
INSERT INTO `book` VALUES (3, '10,11,25,33');
INSERT INTO `book` VALUES (4, 'd');
INSERT INTO `book` VALUES (5, 'e');
SET FOREIGN_KEY_CHECKS = 1;

SELECT
  substring_index( substring_index( a.name, ',', b.help_topic_id + 1 ), ',',- 1 ) AS test_val 
FROM
  book a
join mysql.help_topic b  on b.help_topic_id < ( length(a.name ) - length( REPLACE ( a.name, ',', '' ) ) + 1 )

SELECT
  substring_index( substring_index( a.name, ',', b.help_topic_id + 1 ), ',',- 1 ) AS test_val 
FROM
  book a
join mysql.help_topic b  on b.help_topic_id < ( length(a.name ) - length( REPLACE ( a.name, ',', '' ) ) + 1 )
WHERE  a.id=3

SELECT
  substring_index( substring_index( a.name, ',', b.help_topic_id + 1 ), ',',- 1 ) AS test_val 
FROM
  book a
join mysql.help_topic b  on b.help_topic_id < ( length(a.name ) - length( REPLACE ( a.name, ',', '' ) ) + 1 )
WHERE  a.id=3 AND a.name is not null and a.id  is not null